This article includes discussion of pertussis encephalopathy, acute encephalopathy in whooping cough, pertussis toxin-induced encephalopathy, post-vaccinial encephalopathy, whooping cough encephalopathy, and vaccine encephalopathy. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Pertussis or whooping cough is an important cause of infant death worldwide. Pertussis is caused by the organism Bordetella pertussis, a gram-negative bacillus. Severe complications of pertussis include pneumonia, encephalopathy, and meningoencephalitis. Central hypoventilation secondary to pertussis encephalopathy occurring during childhood has been described in an isolated case. In a study, an increased risk of epilepsy was noted in children with hospital-diagnosed pertussis compared with the general population. Infants who survive critical pertussis illness often have poor neurocognitive development. In the past, several neurologic complications were found to be associated with whole-cell pertussis vaccination, such as acute encephalopathy, seizures, hypotonic-hyporeactive episodes, inconsolable crying, or anaphylactic reactions. Experts now believe that there is no convincing evidence proving an association between the pertussis vaccine and persistent brain damage. Vaccine encephalopathy is, in fact, an inherited genetic defect of the SCN1A gene that codes for the voltage-gated neuronal sodium channel. Pertussis vaccination might trigger earlier onset of Dravet syndrome because of an SCN1A mutation. In fact, children who presented with earlier diagnoses of alleged vaccine encephalopathy in infancy were diagnosed years later with Dravet syndrome. The prenatal maternal tetanus, diphtheria, and acellular pertussis vaccination is safe, and the vaccine is not associated with an increased risk of autism spectrum disorder in offspring. That vaccine triggers autoimmune encephalitis remains unconfirmed. Based on a review of current literature, the author presents an overview focusing on pertussis encephalopathy and vaccine encephalopathy; in addition, he also discusses the epidemiology, pathogenesis, pathology, diagnosis, and treatment of pertussis.

Key points

• Encephalopathy is a rare complication of pertussis.

• Several neurologic complications have been described with the pertussis vaccines, particularly with whole-cell vaccines.

• There is no convincing evidence proving an association between vaccine and persistent brain damage.

In 1640, Guillaume de Baillou provided the first detailed description of whooping cough as a distinct entity, as he described an epidemic in 1578 (Versteegh et al 2005). Kohn suggests that the description of the Perinthus cough by Hippocrates (around 400 BC) might possibly be whooping cough or a mix with other diseases, such as viral respiratory infections. In 1682, Thomas Willis was the first person to recognize the epidemic nature of pertussis. Bordet was credited with first describing the bacteria Bordetella pertussis. In 1900, he observed numerous coccobacilli in respiratory secretions collected from his own daughter who was suffering from pertussis. In 1906 Bordet and Gengou cultured Bordetella pertussis. Encephalopathy was first described as a complication of pertussis infection in 1877. Sydenham first used the term pertussis in 1960. Following the widespread use of whole-cell pertussis vaccines containing diphtheria and tetanus toxoids in the 1940s, the mean incidence rates of pertussis decreased from 150/100,000 to approximately 1/100,000 by 1980. Vaccine encephalopathy was first identified as a major problem with the report of Byers and Moll in 1948. Eight efficacy trials evaluating acellular pertussis vaccines were conducted in the early 1990s; the results were reported in publications from 1995 to 1998. In 1996, less immuno-reactogenic diphtheria, tetanus, and acellular pertussis vaccines were licensed and recommended for routine use in infants and young children, replacing whole-cell pertussis and diphtheria and tetanus toxoid vaccines completely in the United States. Acellular pertussis vaccines were not associated with enhanced risk of neurologic complications.

Pertussis encephalopathy became an issue in United Kingdom in 1975 with the report of 36 children who developed neurologic problems after pertussis vaccination. It was this concern that led to the pertussis epidemic in England as a result of decreased immunization. The British National Childhood Encephalopathy Study was set up in 1976 as an independent scientific enquiry into severe acute neurologic illnesses associated with pertussis vaccine in an attempt to help resolve the issue. The British National Childhood Encephalopathy Study estimated the risk of serious neurologic complications like encephalopathy, unexplained coma, convulsions lasting more than 30 minutes or associated with persistent complications, infantile spasms, and Reye syndrome occurring in previously normal children to be within 7 days of immunization and observed that no close association between vaccination and brain disease existed in most of the cases (Olson 1975; Versteegh et al 2005).

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